1. Technical Field
The present disclosure relates to wireless communication devices, such as wireless transmission devices, that transmit signals of high-frequency waves, such as microwaves, submillimeter waves, or millimeter waves, (hereinafter, referred to as high-frequency signals) and relates to wireless communication systems that include a plurality of such wireless communication devices.
2. Description of the Related Art
In the field of wireless communication using microwave and millimeter-wave bands, high-frequency circuits (hereinafter, referred to as radio-frequency (RF) circuits) are being developed under the complementary metal-oxide semiconductor (CMOS) technology, and the study on reducing the size and the power consumption of RF circuits is being carried out for the commercialization of RF circuits.
For example, in a specific low-power wireless communication device that uses a millimeter-wave band, such as a 79-GHz band, the strength of the transmission waves, that is, the power level of the transmission signals is specified. For example, in a high-frequency range, such as a millimeter-wave band, the threshold voltage of a transistor constituting an integrated-circuit chip (hereinafter, referred to as an IC chip) varies in accordance with a variation in a semiconductor process technology, a variation in the temperature, or a variation in the power-supply voltage, and thus the high-frequency characteristics vary greatly. Accordingly, the power of transmission signals may vary, and thus the power of the transmission signals needs to be controlled. Specifically, the transmission power level needs to be controlled to stay constant by measuring the power level of the transmission signals.
Japanese Unexamined Patent Application Publication No. 5-122087 and Japanese Unexamined Patent Application Publication No. 2009-89202, for example, are known as existing techniques related to a wireless communication device that controls the power level of transmission signals to stay constant. The wireless transmission device described in Japanese Unexamined Patent Application Publication No. 5-122087 changes the power level of a baseband signal by changing a reference voltage applied to a DA converter in accordance with the result of measuring the power level of high-frequency signals and thus controls the transmission power level of the high-frequency signals to stay constant.
In addition, an RF power amplification device described in Japanese Unexamined Patent Application Publication No. 2009-89202 applies, to a RF power amplifier, an automatic power control voltage that is output by an error amplifier to which a negative-feedback circuit and an attenuator are connected in accordance with the result of measuring the power level of high-frequency signals and thus controls the transmission power level of the high-frequency signals to stay constant.